Opamps Engineered for Tomorrow Date dd.mm.yy Manju Khanna

Subject Name: Electronic Circuits Subject Code: 10CS32 Prepared By: Manju Khanna Department: CSE Date:30/8/2014 11/24/2018

Agenda Filters Classification Active Filters First Order Filter Second Order Filter Phase Shifters Instrumentation Amplifier Non-Linear Amplifier Relaxation Oscillator Current to Voltage Converter Voltage to Current Converter

Filters Filters Active Filters Passive Filters

Active Filters : These filters use Active components such as opamps , transistors along with resistor and capacitor. Order of an active filter depends on the number of RC sections used in the filter. Passive Filters: These filters use Passive components such as resistor,capacitor,inductor.

Active Filters They are classified as first order and second order. Order depends on RC sections in the filter. Opamp Filters Low Pass High Pass Band Pass Band Reject

Frequency bands of Filters Band Reject Filter

First Order Filters

Low Pass Filter At low frequencies reactance offered by capacitor is larger than resistance value At high frequencies reactance offered by capacitor is smaller forcing the output to zero. Cut off frequency(fc) fc = ½(pi) R C Where R-resistance C- Capacitance , pi – 22/7 To increase gain of opamp use R2 and R3 resistance as show below: Av = 1 + R3/R2 where Av – gain

Figure shows low pass and High pass filters with gain

Inverting configuration of opamp Low Pass and High Pass Filters

Low Pass Filter fc = ½(pi) R2 C1 Av = - R2/R1 where R2 and C1 are the resistances and capacitances as shown in the figure. High Pass Filter fc = ½(pi) R1 C1 Av = - R2/R1 where R1 and C1 are the resistances and capacitances as shown in the figure.

Second Order Filters Butterworth filters commonly used second order filters Butterworth or Flat Filters Offer a flat pass and stop band response

Low Pass 2nd Order Butterworth Filter Z1=Z2=R Z3=Z4=C High Pass 2nd Order Butterworth Filter Z1=Z2=C Z3=Z4=R fc = ½(pi) RC Pass Band Gain(Av) = 1 + R2/R1

Second Order Band Pass Filters Formed by cascading high pass and low pass filters in series At Low frequencies : C1,C2 offers high reactance At high frequencies :the output is shorted which converts the circuit to an inverting amplifier with zero gain. Intermediate frequencies: the resonant frequency is given by fR=2Q/2(pi) R2 C

Second Order Band Pass Filter With respect to the above figure For C1=C2=C Q= [R1 R2/2R3] ½ Q- Quality Factor C-Capacitance R-Resistance Av = Q/2(pi)R1fR C fR –Resonant frequency

Second Order Band Reject Filter Implemented by summing the output of low pass and high pass filters. At Low frequencies: The output is through the path R1-R2-C3 acts as low pass filter. At High frequencies: The output through path C1-C2-R3 acts as high pass. At Intermediate frequencies: both the filters phase shift the signal and the result net is zero. With reference to the figure: R1=R2=R , R3=R/2 C1=C2=C, C3=2C fR=1/2(pi)RC 0<= R4<=(R1+R2)

Second Order Band Reject Filter

. Phase Shifters Phase shifters shift the angle of an input signal by an angle Ө. There are 2 type: Lagging phase shifter Leading phase shifter Lagging Phase Shifter: Output lags the input by an 0degrees to -180 degrees Leading Phase Shifter: Output leads the input by an 0degree to 180degrees.

.

Instrumentation Amplifier It is a differential amplifier that is optimized for DC performance. It is designed to approach the ideal opamp. It offers: High differential gain High CMRR High Input Impedance low Input offsets and low temperature drifts. .

It consists of 2 stages: Preamplifier stage and difference amplifier stage. The opamp A1 and A2 in the preamplifier stage are in the non-inverting configuration. Provide high gain, high input impedance. Output of both is input to the difference amplifier. The signal at R1 –R2 and R3,R4 are equal. .

. Non-Linear Amplifier The Gain of a non-linear amplifier is a function of the amplitude of the signal. Gain is very large for weak Input. Gain small for large Input signals. A non-linear device is in the feedback path. Weak Input: Diodes act as open circuit. High gain due to minimum feedback. Large Input: Diode offers resistance, short circuit. low gain.

Relaxation Oscillator . Relaxation Oscillator Relaxation oscillator oscillator produces non –sinusoidal signals. Time period is dependent on the charging time of the capacitor. The capacitor is charged through resistance R. Input of opamp at non-inverting input is + Vsat * R1/(R1+R2) Forces the output to =+Vsat. Input of opamp at non-inverting input is - Vsat * R1/(R1+R2) Forces output to -Vsat

Relaxation oscillator . Relaxation oscillator

Current to Voltage Converter . Current to Voltage Converter Current to voltage converter is a transimpedance amplifier. Zero Input and Output impedance.

. Voltage to Current Converter It is transconductance amplifier used for voltage to current converter.